1. Field of the Invention
The present invention relates to a compound bow, and more particularly, to a self-tunable compound bow which can self-align length of cam cables alone so that rotational angles of upper and lower cams become identical when a bowstring has been pulled.
2. Description of the Related Art
Typically, compound bows are configured so that a bowstring may be easily pulled without using a large force and arrow shooting power is increased during shooting, by using an effect of a cam or wheel, to thus result in a fast speed of an arrow and have very strong power, and are widely used mainly for hunting.
As shown in FIGS. 1 and 2, a conventional compound bow is configured to have upper limbs 20 that are coupled to the upper portion of a handle 10 at the center of which a grip portion is formed, and lower limbs 26 coupled to the lower portion of the handle 10. A cut-out portion 21 is formed between the upper limbs 20 whose edges 22 are spaced apart from each other, and a cut-out portion 27 is formed between the lower limbs 26 whose edges 28 are spaced apart from each other. Rotating shafts 70 are horizontally formed through the edges 22 of the upper limbs 20 and the cut-out portion 21, and through the edges 28 of the lower limbs 26 and the cut-out portion 27, respectively. Upper and lower pulleys 30 and 36 are rotatably combined with the respective rotating shafts 70.
A bowstring 50 is wound along a guide groove of each pulley 30 or 36, and the respective ends of the bowstring 50 are combined with each pulley 30 or 36. In addition, a cam 32 or 38 rotating with the pulley 30 or 36 is coupled in each pulley 30 or 36. As the bowstring 50 is pulled, cam cables 40 and 46 are formed so as to be wound on the cams 32 and 38, respectively. One end of each cam cable 40 or 46 is coupled to a pulley 30 or 36 to which each cam 32 or 38 is coupled, and the other end of each cam cable 40 or 46 is coupled to each rotating shaft 70 at both sides of the cut-out portion 21 or 27 of each of the opposing limbs 20 and 26 in the form of Y-shaped buss cables 40a and 46a. 
Further, a cable guard 60 is laterally mounted at one side of a center portion of a handle 10, in which the cable guard 60 pushes the cam cables 40 and 46 to one side of the bowstring 50 so that an arrow is not prevented from being shot during shooting. In addition, a slide 66 is movably mounted on the cable guard 60 in which the cam cables 40 and 46 are inserted into the slide 66.
When the bowstring 50 is pulled in the prior art compound bow that is configured as described above, the lower and upper pulleys 30 and 36 are rotated and thus the cams 32 and 38 coupled to the lower and upper pulleys 30 and 36 are rotated, to thereby wind and pull the cam cables 40 and 46. When the bowstring 50 is released in a let-off state, an arrow obtains a strong driving force by a strong elastic force of the bow which returns to an original position instantaneously.
However, due to the strength of the limbs 20 and 26 or a change in a point at which the bowstring 50 is pulled in the compound bow, the rotational angles of the upper and lower cams 32 and 38 may be changed when the bowstring 50 is pulled and thus is at a let-off state. In this case, since both the two cams 32 and 38 do not become at a let-off state, the original strength of the bow is not exhibited and the accuracy of an arrow is reduced.
As described above, in the case that the rotational angles of the upper and lower cams 32 and 38 are changed, the lengths of the cam cables 40 and 46 may be adjusted in order to set the rotational angles of the upper and lower cams 32 and 38. However, it is difficult to determine difference in the rotational angles of the upper and lower cams 32 and 38, by a bowyer alone. As a result, since it is difficult to adjust the lengths of the cam cables, it is inconvenient for the other person to determine and tell difference in the rotational angles of the upper and lower cams 32 and 38 when a bowyer pulls the bowstring 50.